Optical modulators are used in a variety of applications. Controlled modulation of light is useful in analog systems to produce an output proportional to the input signal. Digital optical systems, such as fiber optic communication systems, use optical modulators to impose digital signals on light. Digital optical modulators as signaling devices may also form the basis for optical memories and general computer devices.
One form of optical modulation is electro-absorption (hereinafter, “EA”) modulation. In conventional EA modulation, EA material is an integral part of the optical waveguide. Consequently, the design of the microwave waveguide is constrained by the optical waveguide design. It is necessary to trade off optical and microwave waveguide design considerations.
As a result, after considering various trade-offs, existing optimized EA modulators are typically 200 μm long or shorter, and the EA layer is a few thousand angstroms thick over the width of the waveguide. At such short interaction lengths, they do not take full advantage of traveling wave interactions. The size of the optical mode is approximately 1 to 2 μm, requiring expansive and precise coupling to single mode optical fibers. The high density of the optical field in the EA layer of an EA modulator of such a small mode also limits the saturation optical power of the modulator typically to a few milliwatts.